As noted in U.S. Pat. No. 3,089,890 to Chapp and Newallis, dihydrocarbylchlorothiophosphates (a.k.a. O,O-dihydrocarbylphosphorochloridothioates), such as diethylchlorothiophosphate are of considerable value as intermediates in the manufacture of pesticidal agents, and can also be used for manufacture of other types useful products.
In the production of dihydrocarbylchlorothiophosphates, small amounts of an undesirable dihydrocarbylpolysulfide coproduct, typically a dihydrocarbyltrisulfide, tend to be formed. Even amounts of less than 0.5 wt % in the dihydrocarbylchlorothiophosphate reaction product is of concern because of its highly disagreeable, persistent odor. Usually still another undesirable coproduct is formed during the production of the dihydrocarbylchlorothiophosphate. This impurity is the oxygen analog of the desired product, i.e., the corresponding dihydrocarbylchlorophosphate, the separation of which is addressed in the foregoing Chapp and Newallis patent. Unfortunately, although this latter impurity can be effectively removed to satisfactorily low levels by the aqueous washing and extraction procedure described in that patent, the Chapp and Newallis procedure described in the patent is incapable of removing the offensive dihydrocarbyltrisulfide impurity to the low levels desired in the final product.
A need thus exists for an effective, commercially feasible way of upgrading the quality of dihydrocarbylchlorothiophosphates by removing therefrom the dihydrocarbylpolysulfide impurities, notably the dihydrocarbyltrisulfide, if not completely, then at least to acceptably low levels. At the same time it would highly advantageous if the procedure would have the capability of concurrently removing the dihydrocarbylchlorophosphate impurity, when copresent, to satisfactorily low levels. It would also be desirable to provide a new, efficient way of removing dihydrocarbylchlorophosphate from crude dihydrocarbylchlorothiophosphates, or at least reducing the dihydrocarbylchlorophosphate impurity content of crude dihydrocarbylchlorothiophosphates, in any situation where no dihydrocarbylpolysulfide impurity is copresent.
In commonly owned copending application Ser. No. 09/249,361, filed Feb. 12, 1999, a process is described in which the above impurities in a crude dihydrocarbylchlorothiophosphate product are removed, if not completely, then at least to acceptably low levels. This is accomplished in that process by use of an aqueous hypochlorite solution as a treating agent for the crude dihydrocarbylchlorothiophosphate product. The application notes that it appears that in situ release of chlorine probably occurs and plays a role in the purification reactions that take place on contacting an aqueous hypochlorite solution with the crude product contaminated with such impurities. While the process described in that application Ls effective in reducing the content of these impurities, loss of some of the desired product can occur. Also the process requires more raw materials, and generates more aqueous waste than desired.